Temperatures across Russia are generally pleasant in May, and warm later in the month without being too hot. You'll need a light jacket and sweater even for the daytime, but nothing extreme.
Average highs are uniformly mild across the major cities of the country, although the further north you go the colder the temperatures, and the longer snow and ice sticks around for. Snowfall is still possible throughout Siberia in May.
In May, you can expect highs of 64° F (18° C) in Moscow, 60° F (16° C) in St. Petersburg, 62° F (17° C) in Irkutsk, and 59° F (15° C) in Vladivostok.
Crowds & Costs
Tourist arrivals pick up from May, as the weather is more comfortable than earlier in the year, and more attractions are open and accessible. But, it's not yet as busy as the summer, which properly starts in June, as temperatures are cooler and most Europeans (and Russians) are not yet on holiday from school and work.
If you want to ride the Trans-Siberian Railway in May, it's a good idea to book your tickets as far in advance as possible. More people take the trip in May than earlier in the year, so demand is higher on the more comfortable trains that tourists usually prefer to take.
Where to Go
In St. Petersburg, the fountains at the Peterhof Palace start up again in May. While this might seem like a minor thing, it means this major attraction starts to look its best again. Other parks and gardens also come to life with flowers and water features.
With overland and air transportation more reliable again in May after the winter (which can bring storms and heavy snow), this is a good month to travel Russia's 'Golden Ring'. A number of old historic cities in western Russia—including Yaroslavl, Kostroma, Suzdal, Sergiev Posad, and Pereslavl-Zalessky—are easily accessible from Moscow and St. Petersburg, and offer a great overview of European Russian culture, history, and architecture. There's no firm list of which cities can be included in a Golden Ring tour, so you can devise an itinerary to suit your time and interests.
May is also a good time to head to Lake Baikal (the world's deepest lake), as well as Irkutsk and Ulan Ude nearby. It can either be reached from western Russia via a flight or on the Trans-Siberian Railway. There may still be large chunks of ice in the lake at this time, and the temperatures are a bit cool, but you'll avoid the larger tour groups that pass through in the summer.
What to Do
May is a good time to do the Trans-Siberian Railway (or part of it, if you prefer). Different classes of trains have different cooling/heating arrangements. By May, most classes have switched off their heating and opened their windows, so you can travel in comfort through a pleasant climate without feeling too hot or cold. (Climate control problems are less of an issue if you travel on a more expensive premium train!)
Events in May
Easter. Russian Orthodox Easter falls in April or May. Locals attend midnight church services and exchange painted eggs.
May Day, 1st May. The international day celebrating the worker is observed in Russia with parades.
Victory Day, 9th May. This national holiday observes the Soviet Union's sacrifices in the Great Patriotic War, aka World War II.
Glinka Festival, Smolensk. This classical music festival held in late May honors Russian composer Mikhail Glinka, and is a good reason to visit the western Russian city.
Traveling to Russia in May? Check out these great itineraries
Highlights of Russia's Capital Cities - 8 Days. Discover the distinct cultural and artistic characters of European Russia's two largest and most vibrant cities.
Russia's Rural Golden Ring - 7 Days. The spring is an ideal time to venture beyond St. Petersburg and Moscow and explore the western Russian rural heartland, with spectacular churches and village architecture, and centuries of history.
History and Art in Russia - 9 Days. Lovers of art and history are in for a treat in Russia, as there's plenty of each. This tour focuses on the historic, artistic, and architectural highlights of Moscow and St. Petersburg, as well as Tolstoy's country home in Tula.